The present invention relates to the forming of a coil spring having pigtails at each end, and more particularly to a machine for efficiently forming the pig tails.
In many instances, it is desirable to have reduced diameter ends or “pigtails” on a wound coil spring. One example application for such springs is in automotive suspension systems. A reduced diameter at one end of the spring can be beneficial for efficiency in spring height and operating travel.
In a typical coil spring forming manufacturing method, a cut-to-length bar is wound around a solid mandrel that sets the inside diameter of the coil spring. One end coil of the spring can be formed smaller than the next coil of the spring using this technique to provide a pigtailed spring. The mandrel for such springs typically has a smaller diameter on one end to form the reduced end of the spring.
It is also beneficial in many circumstances to also reduce the diameter of the opposite end coil of the spring for similar size and performance reasons. A secondary pigtailing operation is performed after the mandrel has been removed. Typically a separate pigtailing machine performs the pigtailing operation.
Conventional pigtailing machines typically include an A head which receives the previously pigtailed coil and a B head which forms the second pigtail coil. Between the heads, are numerous adjustable fixtures, supports, and clamping arrangements. The adjustable components allow a pigtail of a desired shape to be formed onto an opposite end of coil springs of various sizes and shapes.
Disadvantageously, setup for conventional pigtailing machines is quite extensive. Each adjustable component must be accurately and precisely aligned relative the heads. The setup time for each spring type increases the overall production cycle time and results in a lower manufacturing efficiency. Additionally, the adjustable components may shift over time due to the aggressive environment in which a pigtailing machine operates. Shifting in any of the adjustable supports may result in marking of the spring surface which may lead to a stress concentration and potential early fatigue of the spring during service.
Accordingly, it is desirable to provide a pigtailing machine and forming approach that provides for a double pigtail while reducing cycle time, minimizes marking and assures an accurately formed double pigtailed coil spring.